1. Field of the Invention
The present invention relates to a sequence program inputting device in a programmable sequence controller for producing, correcting and editing a sequence program.
2. Description of the Prior Art
The programmable sequence controller (hereinafter referred to as SC) attains functions similar to those of a relay circuit primarily used in a sequence control, using a stored program type general purpose electronic circuit similar to an electronic computer. FIG. 1 shows a configuration of the SC, in which numeral 1 denotes an arithmetic and control unit, numeral 2 denotes a storage unit, numeral 3 denotes an interface unit to a device to be sequence controlled, and numeral 4 denotes a sequence program inputting device from which an operator inputs a sequence program.
A relay ladder diagram as shown in FIG. 2 has been widely used in designing the sequence control. When a two-dimensional image display device such as a CRT display device is used, the ladder diagram can be directly displayed. Thus, by using the ladder diagram for the sequence program inputting device of the SC, those technicians who have been familiar with the ladder diagram will be able to easily input the sequence program when they handle the SC.
The sequence program inputting devices which utilize the two-dimensional image display devices such as CRT display devices have been known in the art. One example thereof is shown in FIG. 3, in which numeral 5 denotes a keyboard from which an operator keys in a sequence program and various operation commands, numeral 6 denotes a control unit for writing the sequence program inputted from the keyboard 5 into a refresh memory 7 and/or into the storage unit 2 of the SC, reading the sequence program from the storage unit 2 and writing it into the refresh memory 7, and executing various commands inputted from the keyboard 5. Numeral 7 denotes the refresh memory in which data to be displayed on a display unit 10 is stored. The data stored therein is sequentially read out at a timing clocked by a display control unit 9 and is converted to characters or figure elements of the ladder diagram by a pattern generator 8, which which the data is displayed on the display unit 10 under the control of the display control unit 9.
The SC usually includes a set of logical operation instructions for executing logical OR and logical AND functions in order to execute the sequence control. An example of a set of such instructions is shown in FIG. 4. In the sequence program inputting device of the construction described above, each of the figure symbols of the ladder diagram shown on the righthand of the chart of FIG. 4 is allocated to one of the logical operation instructions and keys (push buttons) marked with those figure symbols are provided on the keyboard of the program inputting device so that an operator can depress desired figure symbol keys to input the ladder diagram.
FIG. 5 shows an example of the relay sequence program (ladder diagram) inputted in accordance with the above sequence. In FIG. 5, the portions circled by squares correspond to the figure symbol keys on the keyboard of the inputting device. The numerals on the upper right corners of the squares indicate the sequence of the key operation. The figure symbols of the relay contacts or relay coils should be numbered or named, but they are omitted here for the convenience of explanation.
As described above, the figure symbols on the keys have one-to-one correspondence with the instructions of the SC. In this system, each time a figure symbol key is depressed, a corresponding instruction is written into the refresh memory 7 and displayed on the display unit 10, and it is simultaneously written into the storage unit 2 of the SC. Accordingly, in this system, the sequence of key operation is an important factor in inputting and/or correcting the sequence program. In other words, if the keys are depressed in a different sequence, a different ladder diagram will be produced or a ladder diagram which cannot operate correctly will be produced.
Accordingly, in this system, the CRT display device is used in inputting the ladder diagram so that those technicians who have been familiar with the ladder diagram can conveniently handle the SC, but, in actual fact, it inputs the sequence program in the form of one-dimensional image and does not fully and effectively utilize the two-dimensional image. The operator, when inputting the sequence program, must previously draw the ladder diagram on a design sheet and determine the sequence of key operation before he actually inputs the sequence program.